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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"

20212 results found.

  1. EP250827a: Einstein Probe detection of an X-ray transient
  2. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  3. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  4. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  5. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  6. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  7. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  8. EP250821a: MeerKAT radio counterpart
  9. GRB 250823A: COLIBRÍ optical observations
  10. GRB 250823A: SVOM/VT optical observation
  11. GRB 250823A: Swift/UVOT Detection
  12. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  13. GRB 250818B: MeerKAT Detection
  14. GRB 250823A: Enhanced Swift-XRT position
  15. GRB 250823A: LCOGT Optical Detection
  16. GRB 250823A: Liverpool Telescope optical detection
  17. GRB 250823A: Swift detection of a burst
  18. Konus-Wind detection of GRB 250821B
  19. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  20. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  21. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  22. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  23. GRB 250821A: Kilonova-Catcher optical upper limits
  24. GRB 250821A: VLT/FORS2 Optical Observation
  25. GRB 250821B: SVOM/GRM observation
  26. EP250821a: SVOM/VT optical observation
  27. GRB 250821A: NOT z-band upper limit
  28. GRB 250821A: KAIT optical upper limit
  29. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  30. GRB 250821A: Enhanced Swift-XRT position
  31. GRB 250821A: Swift/UVOT Upper Limits
  32. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  33. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  34. GRB 250821A: LCOGT Optical Upper Limits
  35. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  36. GRB 250821A: Swift detection of a burst
  37. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  38. EP250821a: Einstein Probe detection of an X-ray transient
  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: ATLAS pre-discovery limits for AT2025ulz
  42. GRB 250814A: Swift/UVOT Upper Limits
  43. GRB 250813B: Swift/UVOT Upper Limit
  44. IPN triangulation of GRB 250816A (short)
  45. IPN triangulation of GRB 250814C (short)
  46. IPN triangulation of GRB 250804B (short)
  47. GRB 250818B: Kilonova-Catcher optical afterglow detection
  48. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  49. GRB 250818B: Liverpool Telescope optical detections
  50. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  51. GRB 250818A: AstroSat CZTI detection
  52. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  53. GRB 250818B: Swift/UVOT Detection
  54. GRB 250818B: SAO RAS optical observations
  55. GRB 250818B: KAIT optical observations
  56. GRB 250818A: Swift/UVOT Upper Limits
  57. GRB 250818A: Enhanced Swift-XRT position
  58. GRB 250813B: SVOM/ECLAIRs refined analysis
  59. GRB 250818A: Fermi GBM Observation
  60. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  61. GRB 250814A: Further GRAWITA TNG NIR observations
  62. GRB 250818B: SVOM detection of a short burst
  63. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  64. GRB 250818A: Swift detection of a burst
  65. GRB 250816A: SVOM/GRM observation of a short burst
  66. SVOM/sb25081602: detection of a likely X-ray transient
  67. GRB 250813B: Liverpool Telescope optical upper limits
  68. GRB 250814A: Further COLIBRÍ optical upper limit
  69. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  70. GRB 250814A: GRAWITA TNG NIR observations
  71. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  72. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  73. GRB250814A: TRT optical upper limits
  74. GRB 250814B: SVOM/GRM observation
  75. GRB 250813B: SVOM/GRM observation
  76. GRB 250814A: P200/WIRC observations of the afterglow candidate
  77. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  78. GRB 250814A: KAIT optical upper limit
  79. GRB 250814A: Swift-XRT refined Analysis
  80. GRB 250814A: Possible afterglow candidate from P200/WIRC
  81. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  82. GRB 250814A: J-band upper limit from WINTER
  83. GRB 250813B: NOT observations of the optical afterglow
  84. GRB 250814A: COLIBRÍ optical upper limit
  85. GRB 250813A: AstroSat CZTI detection
  86. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  87. GRB 250814A: DDOTI Optical Upper Limit
  88. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  89. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  90. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  91. GRB 250813B: SVOM detection of a bright long burst
  92. EP250812a: Nickel optical upper limit
  93. EP250812a: NOT, NTT, and GS observations
  94. GRB 250812A: Swift/UVOT Detection
  95. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  96. EP250812a: Liverpool Telescope upper limits
  97. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  98. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  99. EP 250812a: GOTO optical upper limit
  100. GRB 250812A: Kilonova-Catcher optical afterglow detection

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