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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').
Advanced Search

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.

Advanced Search Examples (click to copy):

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

19863 results found.

  1. GRB 250813B: Swift/UVOT Upper Limit
  2. IPN triangulation of GRB 250816A (short)
  3. IPN triangulation of GRB 250814C (short)
  4. IPN triangulation of GRB 250804B (short)
  5. GRB 250818B: Kilonova-Catcher optical afterglow detection
  6. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  7. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  8. GRB 250818B: Swift/UVOT Detection
  9. GRB 250818B: SAO RAS optical observations
  10. GRB 250818B: KAIT optical observations
  11. GRB 250818A: Swift/UVOT Upper Limits
  12. GRB 250818A: Enhanced Swift-XRT position
  13. GRB 250813B: SVOM/ECLAIRs refined analysis
  14. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  15. GRB 250814A: Further GRAWITA TNG NIR observations
  16. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  17. GRB 250818A: Swift detection of a burst
  18. GRB 250816A: SVOM/GRM observation of a short burst
  19. GRB 250813B: Liverpool Telescope optical upper limits
  20. GRB 250814A: Further COLIBRÍ optical upper limit
  21. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  22. GRB 250814A: GRAWITA TNG NIR observations
  23. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  24. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  25. GRB250814A: TRT optical upper limits
  26. GRB 250814B: SVOM/GRM observation
  27. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  28. GRB 250814A: P200/WIRC observations of the afterglow candidate
  29. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  30. GRB 250814A: KAIT optical upper limit
  31. GRB 250814A: Swift-XRT refined Analysis
  32. GRB 250814A: Possible afterglow candidate from P200/WIRC
  33. GRB 250813B: Fermi GBM Observation
  34. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  35. GRB 250814A: J-band upper limit from WINTER
  36. IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
  37. GRB 250813B: NOT observations of the optical afterglow
  38. GRB 250814A: COLIBRÍ optical upper limit
  39. GRB 250813A: AstroSat CZTI detection
  40. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  41. GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752
  42. GRB 250814A: DDOTI Optical Upper Limit
  43. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  44. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  45. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  46. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  47. GRB 250813B: SVOM detection of a bright long burst
  48. LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
  49. EP250812a: Nickel optical upper limit
  50. EP250812a: NOT, NTT, and GS observations
  51. GRB 250812A: Swift/UVOT Detection
  52. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  53. EP250812a: Liverpool Telescope upper limits
  54. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  55. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  56. EP 250812a: GOTO optical upper limit
  57. GRB 250812A: Kilonova-Catcher optical afterglow detection
  58. EP250812a: Swift-XRT counterpart detection
  59. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  60. EP250812a: Einstein Probe detection of an X-ray transient
  61. GRB 250812A: Swift-XRT afterglow detection
  62. GRB 250812A: TRT likely optical counterpart detection
  63. IceCube-Cascade 250809A: Upper limits from a search for additional neutrino events in IceCube
  64. Fermi-LAT Gamma-ray Observations of IceCube-250804A
  65. GRB 250809A: Swift/UVOT Detection
  66. GRB 250809A: Swift-XRT refined Analysis
  67. GRB 250809A: LCOGT Optical Upper Limits
  68. GRB 250808A: VLT X-shooter candidate counterpart
  69. GRB 250809A: Swift detection of a gamma ray burst
  70. GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  71. Konus-Wind detection of GRB 250807A
  72. GRB 250807B: Swift/UVOT Detection
  73. GRB 250807B: Kilonova-Catcher optical afterglow detection
  74. IceCube-250804A: Upper limits from a search for additional neutrino events in IceCube
  75. GRB 250807A: Swift/UVOT Detection
  76. GRB 250807B: VLT/X-Shooter spectroscopic redshift z = 1.522
  77. GRB 250806A: SVOM/ECLAIRs refined analysis
  78. EP250807a: NTT z-band optical upper limit
  79. GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
  80. GRB 250807A: SVOM/GRM observation
  81. GRB 250807A: AstroSat CZTI detection of bright long burst
  82. EP250807a: EP-WXT detection of a fast X-ray transient
  83. EP 250807.979: GOTO optical upper limit
  84. EP250807a: COLIBRÍ optical upper limit
  85. GRB 250807B: Enhanced Swift-XRT position
  86. GRB 250807A: Enhanced Swift-XRT position
  87. IceCube-Cascade 250804A: Upper limits from a search for additional neutrino events in IceCube
  88. GRB 250807B: Swift detection of a burst with an optical counterpart.
  89. GRB 250805A: Kilonova-Catcher optical upper limits
  90. GRB 250805A: Swift/UVOT Upper Limits
  91. GRB 250806A: Swift/UVOT U-band detection
  92. EP250806a: Liverpool telescope optical upper limit
  93. GRB 250807A: Swift detection of a burst with an optical counterpart
  94. GRB 250806A: EP-FXT observation
  95. EP250806a: refined analysis of the EP-WXT and EP-FXT observations
  96. EP250806a: SVOM /VT optical candidate
  97. GRB 250806A: J-band upper limit from WINTER
  98. GRB 250806A: KAIT optical upper limit
  99. EP250806a: COLIBRÍ optical upper limit
  100. GRB 250806A: Kilonova-Catcher optical upper limits

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