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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"

7392 results found.

  1. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  2. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  3. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  4. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  5. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  6. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  7. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  8. GRB 250823A: Swift detection of a burst
  9. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  10. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  11. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  12. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  13. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  14. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  15. GRB 250806A: Gemini observations of host galaxy candidate
  16. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  17. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  18. GRB 250821A: KAIT optical upper limit
  19. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  20. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  21. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  22. GRB 250821A: Swift detection of a burst
  23. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  24. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  25. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  26. GRB 250818B: Kilonova-Catcher optical afterglow detection
  27. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  28. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  29. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  30. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  31. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  32. GRB 250818B: Keck redshift of the optical afterglow
  33. LIGO/Virgo/KAGRA S250818t: Updated Sky localization
  34. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  35. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  36. GRB 250818B: Swift-XRT afterglow detection
  37. GRB 250818B: GOTO optical counterpart candidate
  38. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  39. GRB 250818A: Swift detection of a burst
  40. sb25081602: Swift-XRT observations
  41. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  42. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  43. GRB 250814A: P200/WIRC observations of the afterglow candidate
  44. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  45. GRB 250814A: KAIT optical upper limit
  46. GRB 240814A: Fermi GBM Observation
  47. GRB 250814A: Possible afterglow candidate from P200/WIRC
  48. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  49. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  50. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  51. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  52. LIGO/Virgo/KAGRA S250813k: Updated Sky localization
  53. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  54. EP250812a: Liverpool Telescope upper limits
  55. IceCube-250813A - IceCube observation of a high-energy neutrino candidate track-like event
  56. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  57. GRB 250812A: Swift ToO observations
  58. EP 250812a: GOTO optical upper limit
  59. GRB 250812A: Kilonova-Catcher optical afterglow detection
  60. EP250812a: Swift-XRT counterpart detection
  61. LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification
  62. LIGO/Virgo/KAGRA S250810ck: Identification of a GW compact binary merger candidate
  63. GRB 250808A: VLT X-shooter candidate counterpart
  64. GRB 250809A: Swift detection of a gamma ray burst
  65. GRB 250808A: Swift-XRT candidate counterpart detection
  66. GRB 250806A: SVOM/MXT refined analysis
  67. GRB 250806A: SVOM/ECLAIRs refined analysis
  68. GRB 250806A: NOT z-band upper limit and host galaxy candidate
  69. EP 250807.979: GOTO optical upper limit
  70. GRB 250807B: Swift detection of a burst with an optical counterpart.
  71. GRB 250805A: Kilonova-Catcher optical upper limits
  72. EP250806a:SVOM/VT refined analysis
  73. EP250806a: Liverpool telescope optical upper limit
  74. GRB 250807A: Swift detection of a burst with an optical counterpart
  75. EP250806a: Earlier Detection of the VT Candidate by COLIBRÍ and LS
  76. EP250806a: SVOM /VT optical candidate
  77. GRB 250806A: KAIT optical upper limit
  78. GRB 250806A: SVOM/VT refined analysis
  79. IceCube-250804A - IceCube observation of a high-energy neutrino candidate track-like event
  80. GRB 250804B: Tiled Swift observations
  81. LIGO/Virgo/KAGRA S250802dn: Updated Sky localization
  82. LIGO/Virgo/KAGRA S250802dn: Identification of a GW compact binary merger candidate
  83. The EP-WXT trigger 01709198202 is likely a flaring star
  84. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
  85. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  86. LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
  87. LIGO/Virgo/KAGRA S250727dc: DECam DESGW Epoch 1 Candidates
  88. LIGO/Virgo/KAGRA S250725j: DECam DESGW Epoch 1-2 Candidates
  89. LIGO/Virgo/KAGRA S250726ak: Upper limits from Swift/BAT-GUANO
  90. LIGO/Virgo/KAGRA S250725l: Upper limits from Swift/BAT-GUANO
  91. LIGO/Virgo/KAGRA S250727dc: Upper limits from Swift/BAT-GUANO
  92. GRB 250727A: EP-FXT follow-up observation
  93. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  94. LIGO/Virgo/KAGRA S250727dc: Updated Sky localization
  95. GRB 250728A: Swift ToO observations
  96. LIGO/Virgo/KAGRA S250727cl: Updated Sky localization
  97. GRB 250727A: EP-FXT counterpart detection
  98. GRB 250727A: Swift-XRT observations
  99. LIGO/Virgo/KAGRA S250727dc: Identification of a GW compact binary merger candidate
  100. LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate

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