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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"

7408 results found.

  1. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  2. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  3. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  4. GRB 250830B: Swift ToO observations
  5. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  6. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  7. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  8. EP250828a: Optical counterpart detection with Kinder observations
  9. EP250828a: Liverpool Telescope upper limits
  10. EP250828a: NOT optical counterpart confirmation
  11. EP250828a: SVOM/VT optical candidate
  12. EP250828a: Optical upper limit with Kinder observations
  13. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  14. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  15. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  16. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  17. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  18. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  19. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  20. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  21. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  22. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  23. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  24. GRB 250823A: Swift detection of a burst
  25. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  26. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  27. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  28. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  29. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  30. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  31. GRB 250806A: Gemini observations of host galaxy candidate
  32. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  33. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  34. GRB 250821A: KAIT optical upper limit
  35. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  36. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  37. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  38. GRB 250821A: Swift detection of a burst
  39. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  40. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  41. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  42. GRB 250818B: Kilonova-Catcher optical afterglow detection
  43. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  44. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  45. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  46. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  47. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  48. GRB 250818B: Keck redshift of the optical afterglow
  49. LIGO/Virgo/KAGRA S250818t: Updated Sky localization
  50. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  51. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  52. GRB 250818B: Swift-XRT afterglow detection
  53. GRB 250818B: GOTO optical counterpart candidate
  54. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  55. GRB 250818A: Swift detection of a burst
  56. sb25081602: Swift-XRT observations
  57. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  58. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  59. GRB 250814A: P200/WIRC observations of the afterglow candidate
  60. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  61. GRB 250814A: KAIT optical upper limit
  62. GRB 240814A: Fermi GBM Observation
  63. GRB 250814A: Possible afterglow candidate from P200/WIRC
  64. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  65. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  66. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  67. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  68. LIGO/Virgo/KAGRA S250813k: Updated Sky localization
  69. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  70. EP250812a: Liverpool Telescope upper limits
  71. IceCube-250813A - IceCube observation of a high-energy neutrino candidate track-like event
  72. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  73. GRB 250812A: Swift ToO observations
  74. EP 250812a: GOTO optical upper limit
  75. GRB 250812A: Kilonova-Catcher optical afterglow detection
  76. EP250812a: Swift-XRT counterpart detection
  77. LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification
  78. LIGO/Virgo/KAGRA S250810ck: Identification of a GW compact binary merger candidate
  79. GRB 250808A: VLT X-shooter candidate counterpart
  80. GRB 250809A: Swift detection of a gamma ray burst
  81. GRB 250808A: Swift-XRT candidate counterpart detection
  82. GRB 250806A: SVOM/MXT refined analysis
  83. GRB 250806A: SVOM/ECLAIRs refined analysis
  84. GRB 250806A: NOT z-band upper limit and host galaxy candidate
  85. EP 250807.979: GOTO optical upper limit
  86. GRB 250807B: Swift detection of a burst with an optical counterpart.
  87. GRB 250805A: Kilonova-Catcher optical upper limits
  88. EP250806a:SVOM/VT refined analysis
  89. EP250806a: Liverpool telescope optical upper limit
  90. GRB 250807A: Swift detection of a burst with an optical counterpart
  91. EP250806a: Earlier Detection of the VT Candidate by COLIBRÍ and LS
  92. EP250806a: SVOM /VT optical candidate
  93. GRB 250806A: KAIT optical upper limit
  94. GRB 250806A: SVOM/VT refined analysis
  95. IceCube-250804A - IceCube observation of a high-energy neutrino candidate track-like event
  96. GRB 250804B: Tiled Swift observations
  97. LIGO/Virgo/KAGRA S250802dn: Updated Sky localization
  98. LIGO/Virgo/KAGRA S250802dn: Identification of a GW compact binary merger candidate
  99. The EP-WXT trigger 01709198202 is likely a flaring star
  100. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm

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