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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
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To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

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subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

7412 results found.

  1. IceCube-250831A - IceCube observation of a high-energy neutrino candidate track-like event
  2. GRB 250831A: Swift-XRT counterpart detection
  3. GRB 250831A: SVOM/VT upper limit with VHF data
  4. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  5. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  6. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  7. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  8. GRB 250830B: Swift ToO observations
  9. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  10. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  11. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  12. EP250828a: Optical counterpart detection with Kinder observations
  13. EP250828a: Liverpool Telescope upper limits
  14. EP250828a: NOT optical counterpart confirmation
  15. EP250828a: SVOM/VT optical candidate
  16. EP250828a: Optical upper limit with Kinder observations
  17. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  18. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  19. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  20. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  21. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  22. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  23. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  24. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  25. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  26. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  27. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  28. GRB 250823A: Swift detection of a burst
  29. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  30. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  31. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  32. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  33. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  34. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  35. GRB 250806A: Gemini observations of host galaxy candidate
  36. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  37. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  38. GRB 250821A: KAIT optical upper limit
  39. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  40. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  41. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  42. GRB 250821A: Swift detection of a burst
  43. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  44. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  45. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  46. GRB 250818B: Kilonova-Catcher optical afterglow detection
  47. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  48. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  49. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  50. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  51. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  52. GRB 250818B: Keck redshift of the optical afterglow
  53. LIGO/Virgo/KAGRA S250818t: Updated Sky localization
  54. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  55. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  56. GRB 250818B: Swift-XRT afterglow detection
  57. GRB 250818B: GOTO optical counterpart candidate
  58. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  59. GRB 250818A: Swift detection of a burst
  60. sb25081602: Swift-XRT observations
  61. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  62. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  63. GRB 250814A: P200/WIRC observations of the afterglow candidate
  64. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  65. GRB 250814A: KAIT optical upper limit
  66. GRB 240814A: Fermi GBM Observation
  67. GRB 250814A: Possible afterglow candidate from P200/WIRC
  68. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  69. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  70. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  71. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  72. LIGO/Virgo/KAGRA S250813k: Updated Sky localization
  73. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  74. EP250812a: Liverpool Telescope upper limits
  75. IceCube-250813A - IceCube observation of a high-energy neutrino candidate track-like event
  76. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  77. GRB 250812A: Swift ToO observations
  78. EP 250812a: GOTO optical upper limit
  79. GRB 250812A: Kilonova-Catcher optical afterglow detection
  80. EP250812a: Swift-XRT counterpart detection
  81. LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification
  82. LIGO/Virgo/KAGRA S250810ck: Identification of a GW compact binary merger candidate
  83. GRB 250808A: VLT X-shooter candidate counterpart
  84. GRB 250809A: Swift detection of a gamma ray burst
  85. GRB 250808A: Swift-XRT candidate counterpart detection
  86. GRB 250806A: SVOM/MXT refined analysis
  87. GRB 250806A: SVOM/ECLAIRs refined analysis
  88. GRB 250806A: NOT z-band upper limit and host galaxy candidate
  89. EP 250807.979: GOTO optical upper limit
  90. GRB 250807B: Swift detection of a burst with an optical counterpart.
  91. GRB 250805A: Kilonova-Catcher optical upper limits
  92. EP250806a:SVOM/VT refined analysis
  93. EP250806a: Liverpool telescope optical upper limit
  94. GRB 250807A: Swift detection of a burst with an optical counterpart
  95. EP250806a: Earlier Detection of the VT Candidate by COLIBRÍ and LS
  96. EP250806a: SVOM /VT optical candidate
  97. GRB 250806A: KAIT optical upper limit
  98. GRB 250806A: SVOM/VT refined analysis
  99. IceCube-250804A - IceCube observation of a high-energy neutrino candidate track-like event
  100. GRB 250804B: Tiled Swift observations

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